Revert "Raise minimum supported Apple OS versions (rust-random#388)"

This reverts commit 5fe3c8e.

Author: sammoore

CHANGELOG.md

@@ -4,6 +4,11 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/)
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [master]
+### Changed
+
+- Reverted "Raise minimum supported Apple OS versions to macOS 10.12 and iOS 10 [#388]"
+
 ## [0.2.12] - 2024-01-09
 ### Fixed
 - Custom backend for targets without atomics [#385]

src/apple-other.rs

@@ -1,21 +1,24 @@
-//! Implementation for iOS, tvOS, and watchOS where `getentropy` is unavailable.
+// Copyright 2018 Developers of the Rand project.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// https://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+//! Implementation for iOS
 use crate::Error;
-use core::{ffi::c_void, mem::MaybeUninit};
+use core::{ffi::c_void, mem::MaybeUninit, ptr::null};
 
-// libsystem contains the libc of Darwin, and every binary ends up linked against it either way. This
-// makes it a more lightweight choice compared to `Security.framework`.
+#[link(name = "Security", kind = "framework")]
 extern "C" {
-    // This RNG uses a thread-local CSPRNG to provide data, which is seeded by the operating system's root CSPRNG.
-    // Its the best option after `getentropy` on modern Darwin-based platforms that also avoids the
-    // high startup costs and linking of Security.framework.
-    //
-    // While its just an implementation detail, `Security.framework` just calls into this anyway.
-    fn CCRandomGenerateBytes(bytes: *mut c_void, size: usize) -> i32;
+    fn SecRandomCopyBytes(rnd: *const c_void, count: usize, bytes: *mut u8) -> i32;
 }
 
 pub fn getrandom_inner(dest: &mut [MaybeUninit<u8>]) -> Result<(), Error> {
-    let ret = unsafe { CCRandomGenerateBytes(dest.as_mut_ptr() as *mut c_void, dest.len()) };
-    // kCCSuccess (from CommonCryptoError.h) is always zero.
+    // Apple's documentation guarantees kSecRandomDefault is a synonym for NULL.
+    let ret = unsafe { SecRandomCopyBytes(null(), dest.len(), dest.as_mut_ptr() as *mut u8) };
+    // errSecSuccess (from SecBase.h) is always zero.
     if ret != 0 {
         Err(Error::IOS_SEC_RANDOM)
     } else {

src/error.rs

@@ -30,9 +30,7 @@ impl Error {
     pub const ERRNO_NOT_POSITIVE: Error = internal_error(1);
     /// Encountered an unexpected situation which should not happen in practice.
     pub const UNEXPECTED: Error = internal_error(2);
-    /// Call to [`CCRandomGenerateBytes`](https://opensource.apple.com/source/CommonCrypto/CommonCrypto-60074/include/CommonRandom.h.auto.html) failed
-    /// on iOS, tvOS, or waatchOS.
-    // TODO: Update this constant name in the next breaking release.
+    /// Call to iOS [`SecRandomCopyBytes`](https://developer.apple.com/documentation/security/1399291-secrandomcopybytes) failed.
     pub const IOS_SEC_RANDOM: Error = internal_error(3);
     /// Call to Windows [`RtlGenRandom`](https://docs.microsoft.com/en-us/windows/win32/api/ntsecapi/nf-ntsecapi-rtlgenrandom) failed.
     pub const WINDOWS_RTL_GEN_RANDOM: Error = internal_error(4);

src/lib.rs

@@ -6,8 +6,8 @@
 //! | ----------------- | ------------------ | --------------
 //! | Linux, Android    | `*‑linux‑*`        | [`getrandom`][1] system call if available, otherwise [`/dev/urandom`][2] after successfully polling `/dev/random`
 //! | Windows           | `*‑windows‑*`      | [`BCryptGenRandom`]
-//! | macOS             | `*‑apple‑darwin`   | [`getentropy`][3]
-//! | iOS, tvOS, watchOS | `*‑apple‑ios`, `*-apple-tvos`, `*-apple-watchos` | [`CCRandomGenerateBytes`]
+//! | macOS             | `*‑apple‑darwin`   | [`getentropy`][3] if available, otherwise [`/dev/urandom`][4] (identical to `/dev/random`)
+//! | iOS, tvOS, watchOS | `*‑apple‑ios`, `*-apple-tvos`, `*-apple-watchos` | [`SecRandomCopyBytes`]
 //! | FreeBSD           | `*‑freebsd`        | [`getrandom`][5] if available, otherwise [`kern.arandom`][6]
 //! | OpenBSD           | `*‑openbsd`        | [`getentropy`][7]
 //! | NetBSD            | `*‑netbsd`         | [`getrandom`][16] if available, otherwise [`kern.arandom`][8]
@@ -171,7 +171,7 @@
 //! [`BCryptGenRandom`]: https://docs.microsoft.com/en-us/windows/win32/api/bcrypt/nf-bcrypt-bcryptgenrandom
 //! [`Crypto.getRandomValues`]: https://www.w3.org/TR/WebCryptoAPI/#Crypto-method-getRandomValues
 //! [`RDRAND`]: https://software.intel.com/en-us/articles/intel-digital-random-number-generator-drng-software-implementation-guide
-//! [`CCRandomGenerateBytes`]: https://opensource.apple.com/source/CommonCrypto/CommonCrypto-60074/include/CommonRandom.h.auto.html
+//! [`SecRandomCopyBytes`]: https://developer.apple.com/documentation/security/1399291-secrandomcopybytes?language=objc
 //! [`cprng_draw`]: https://fuchsia.dev/fuchsia-src/zircon/syscalls/cprng_draw
 //! [`crypto.randomFillSync`]: https://nodejs.org/api/crypto.html#cryptorandomfillsyncbuffer-offset-size
 //! [`esp_fill_random`]: https://docs.espressif.com/projects/esp-idf/en/latest/esp32/api-reference/system/random.html#_CPPv415esp_fill_randomPv6size_t
@@ -242,6 +242,7 @@ cfg_if! {
         #[path = "apple-other.rs"] mod imp;
     } else if #[cfg(target_os = "macos")] {
         mod util_libc;
+        mod use_file;
         #[path = "macos.rs"] mod imp;
     } else if #[cfg(target_os = "openbsd")] {
         mod util_libc;

src/macos.rs

@@ -1,18 +1,36 @@
+// Copyright 2019 Developers of the Rand project.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// https://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
 //! Implementation for macOS
-use crate::{util_libc::last_os_error, Error};
-use core::mem::MaybeUninit;
+use crate::{
+    use_file,
+    util_libc::{last_os_error, Weak},
+    Error,
+};
+use core::mem::{self, MaybeUninit};
 
-extern "C" {
-    // Supported as of macOS 10.12+.
-    fn getentropy(buf: *mut u8, size: libc::size_t) -> libc::c_int;
-}
+type GetEntropyFn = unsafe extern "C" fn(*mut u8, libc::size_t) -> libc::c_int;
 
 pub fn getrandom_inner(dest: &mut [MaybeUninit<u8>]) -> Result<(), Error> {
-    for chunk in dest.chunks_mut(256) {
-        let ret = unsafe { getentropy(chunk.as_mut_ptr() as *mut u8, chunk.len()) };
-        if ret != 0 {
-            return Err(last_os_error());
+    // getentropy(2) was added in 10.12, Rust supports 10.7+
+    static GETENTROPY: Weak = unsafe { Weak::new("getentropy\0") };
+    if let Some(fptr) = GETENTROPY.ptr() {
+        let func: GetEntropyFn = unsafe { mem::transmute(fptr) };
+        for chunk in dest.chunks_mut(256) {
+            let ret = unsafe { func(chunk.as_mut_ptr() as *mut u8, chunk.len()) };
+            if ret != 0 {
+                return Err(last_os_error());
+            }
         }
+        Ok(())
+    } else {
+        // We fallback to reading from /dev/random instead of SecRandomCopyBytes
+        // to avoid high startup costs and linking the Security framework.
+        use_file::getrandom_inner(dest)
     }
-    Ok(())
 }

src/use_file.rs

@@ -1,3 +1,11 @@
+// Copyright 2018 Developers of the Rand project.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// https://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
 //! Implementations that just need to read from a file
 use crate::{
     util_libc::{open_readonly, sys_fill_exact},
@@ -12,7 +20,7 @@ use core::{
 // We prefer using /dev/urandom and only use /dev/random if the OS
 // documentation indicates that /dev/urandom is insecure.
 // On Solaris/Illumos, see src/solaris_illumos.rs
-// On Dragonfly, Haiku, and QNX Neutrino the devices are identical.
+// On Dragonfly, Haiku, macOS, and QNX Neutrino the devices are identical.
 #[cfg(any(target_os = "solaris", target_os = "illumos"))]
 const FILE_PATH: &str = "/dev/random\0";
 #[cfg(any(
@@ -22,6 +30,7 @@ const FILE_PATH: &str = "/dev/random\0";
     target_os = "redox",
     target_os = "dragonfly",
     target_os = "haiku",
+    target_os = "macos",
     target_os = "nto",
 ))]
 const FILE_PATH: &str = "/dev/urandom\0";